1. Field of the Invention
This invention relates to improvements in current source circuits, and more particularly to improvements in current source circuits that provide a current that is proportional to absolute temperature (PTAT).
2. Relevant Background Information
Current source circuits that provide a current that is proportional to absolute temperature have many uses. In the past, such circuits suffered numerous deficiencies.
High output impedance, cascode current mirrors were necessary to force equal currents in two bipolar transistors of different emitter areas, thereby increasing the minimum operating supply. Also, reliable start-up was not enjoyed under all conditions. When a start-up circuitry was present, it had to be disconnected from the circuit not to affect the output current value when an equilibrium was reached. Sensing of that equilibrium was also difficult to implement in a reliable way. Other shortcomings of the classical solutions were the use of operational amplifiers, or current gain dependent output.